The present invention pertains to the field of photocomposing or phototypesetting machines. Photocomposing machines in the prior art have generally provided a disc or reel which contains negatives of the characters to be printed. Selected characters are projected, one at a time, onto a film or other light sensitive material which may be advanced for each character. The film is subsequently developed to obtain the desired printed legend. Alternatively, in some prior art machines the characters are imaged on a portion of the film within a development cell, and development takes place substantially simultaneously with exposure.
U.S. Pat. Nos. 2,742,831, 3,308,732 and 3,581,632 are examples of machines which use a disc type font which is rotated to align the desired character with the optical path. U.S. Pat. No. 3,115,815 shows an example of a machine using a film strip type font wound on a pair of reels. One disadvantage of these prior art devices is the amount of difficulty and time required in changing from one selected character to another. With a film strip type font wound on reels, it is necessary to crank through most of the font when changing from a character that happens to be at one end of the font, to another which happens to be at the other end of the font. All the while during the cranking, the operator must be watching the characters as they flash past the printing zone under the safe light, until the desired character is reached, because there is no way to go directly from one character to another. This can be annoying with alphabetic characters which follow in known sequence and it can be extremely difficult with characters such as punctuation marks, because the operator might not always remember where certain punctuation marks are on the film strip in relation to other characters. This can lead to a character by character search through a major portion of the font strip.
A similar difficulty exists with disc type fonts, although the situation can be somewhat alleviated since there may be a choice of going either backwards or forwards when changing characters, thus reducing the number of characters that must be passed by on the way to the desired character. Still there is the problem of locating punctuation marks or miscellaneous characters which are not in a logical alphabetical sequence. Since character changes are required many times for a typical job, simplification of character selection can lead to much greater efficiency in the long run.
In U.S. Pat. No. 2,537,069, a fiche-like character sheet is proposed, but the full potential and benefits of a well developed fiche-type system are not realized. In that Patent, the characters are still basically arranged in linear form on the character sheet, thus necessitating long moves when going from the beginning to the end of the alphabet. A pointer and a chart are provided to assist the operator in selecting the proper character, but the character sheet and the chart are not interconnected or spacially fixed with respect to each other. Thus, when the character sheet must be changed to bring in other characters or symbols, both the character sheet and the chart might have to be changed. They will also have to be accurately realigned with respect to each other to insure accuracy in the machine.
Other problems or shortcomings existing in prior art machines involve undue complexities in operation or construction. In some machines, changing of the magnification ratio involves awkward manual readjustments and refocusing. In other machines, separate safe lamps and exposure lamps are provided, or else movable safe light filters are provided for moving to and from the optical path. In either case, the mechanical and optical design of the system is made more difficult or expensive.